Hydrolysis of aromatic dinitriles

ABSTRACT

A PROCESS FOR THE PREPARATION OF AN AROMATIC ACID SUCH AS TEREPHTHALIC ACID BY HYDROLYSIS OF TEREPHTHALONITRILE WHICH COMPRISES SUBJECTING TEREPHTHALONITRILE TO AQUEOUS HYDROLYSIS IN A CLOSED REACTOR AT 200*C. TO 300*C. UNTIL A HYDROLYSIS EQUILBRIUM IS OBTAINED, VENTING THE CLOSED SYSTEM TO REMOVE MORE THAN 50% OF A VAILABLE, AMMONIA, ADJUSTING THE VENTER SYSTEM TO A MOLALITY OF TEREPHTHALATE FROM 1.5 TO 2.5, SATURATING THE SYSTEM WITH CARBON DIOXIDE, AND ISOLATING THE PRECITATED TERPHTHALIC ACID BY SEPARATION UNDER A PRESSURE OF ABOUT 50 TO ABOUT 900 P.S.I.G.

United States Patent 3,781,343 HYDROLYSIS OF AROMATIC DINITRILES RichardV. Norton, Wilmington, Del., assignor to Sun Research and DevelopmentCo., St. Davids, Pa. No Drawing. Filed Apr. 12, 1973, Ser. No. 350,433Int. Cl. C07c 63/100, 63/26 US. Cl. 260515 P 4 Claims ABSTRACT OF THEDISCLOSURE A process for the preparation of an aromatic acid such asterephthalic acid by hydrolysis of terephthalonitrile which comprisessubjecting terephthalonitrile to aqueous hydrolysis in a closed reactorat 200 C. to 300 C. until a hydrolysis equilibrium is obtained, ventingthe closed system to remove more than 50% of available, ammonia,adjusting the venter system to a molality of terephthalate from 1.5 to2.5, saturating the system with carbon dioxide, and isolating theprecipitated terephthalic acid by separation under a pressure of about50 to about 900 p.s.i.g.

It is known in the art to treat aqueous solutions of alkali metal saltsof terephthalic acids with carbon dioxide under pressure and to separatethe terephthalic acid which precipitates. The alkali metalterephthalates are obtained by the Henkel reaction which involvesisomerization of an alkali metal salt (generally potassium) ofisophthalic acid or a disproportionation of potassium benzoate. Aqueoussolutions of potassium terephthalate so obtained have been treated withCO to obtain the free acid. US. 3,579,572 describes the precipitation ofterephthalic acid by C0 treatment of a lithium or magnesium saltsolution of the acid. A more recent patent (US. 3,632,635) describes theCO treatment of alkali metal salts of terephthalic acid which areobtained by the hydrolysis of terephthalonitrile in the presence of analkali metal bicarbonate, this treatment producing the alkali metalmonosalt which is subsequently treated to obtain free acid. It is alsoknown from the article by Hajek et a1. (Coll. Czechoslov. Chem. Commun.36, 85, 1971) that when carbon monoxide is introduced into a saturatedaqueous solution of diammonium terephthalate at 25 C. the product whichprecipitates is monoammonium terephthalate.

Terephthalic acid is a well known commodity useful as an intermediate topolyester fibers and when employed for such use it must be of very highpurity. The preparation of terephthalic acid by ammoxidation of p-xyleneis a useful route, but hydrolysis of the nitrile to pure acid cannotreadily be achieved because nitrogen bodies which are hydrolysisintermediates contaminate the final product and these bodies areresistant to removal by solvent extraction or by other conventionaltechniques.

It has now been found that a very high purity aromatic dicarboxylic acidsuch as terephthalic acid may be obtained through theammoxidation-nitrile hydrolysis route, and in accord with the process ofthis invention, an aromatic dinitrile obtained by ammoxidation issubjected to an aqueous hydrolysis in a closed reactor at a temperaturebetween about 200 C. and about 300 C. until a hydrolysis equilibrium isobtained, venting the closed system to remove more than 50% of availableammonia, adjusting the vented system to a molality of aromatic acidproduct from about 1.5 to about 2.5, saturating the system with carbondioxide, and separating the precipitated aromatic acid under pressure ofcarbon dioxide at about 50 to about 900 p.s.i.g.

As indicated, the process is operable with aromatic dinitriles,particularly those of the benzene and naphthalene series. Thus, forexample, operable dinitriles include phthalonitrile, isophthalonitrile,terephthalonitrile, 2,6-di- 3,781,343 Patented Dec. 25, 1973cyanonaphthalene, 1,5-dicyanonaphthalene and the like. The followingdiscussion, however, will use the preferred terephthalonitrile toillustrate the process.

The terephthalonitrile to be hydrolyzed in accord with the invention isfed into a closed hydrolytic chamber where hydrolysis occurs at atemperature between about 200 and 300 C. under autogeneous pressure, thepressure actually rising to about 400 to about 1200 p.s.i.g. In thisreactor, the hydrolysis proceeds until an equilibrium is reached whichrequires about 0.5 to about 3 hours. The hydrolysis products in theequilibrium mixture will consist essentially of the ammonium salt of4-cyanobenzoic acid, 4-cyanobenzamide, terephthalamide and the ammoniumsalts of terephthalic and terephthalamic acids. It will be understoodthat the hydrolysis may be carried out with or without catalysts (e.g.,an alkaline material such as alkali, alkaline earth or ammoniumhydroxide, carbonates, etc.), but a preferred technique is to use anoncatalytic hydrolysis system. After the equilibrium is established, itis shifted by venting the ammonia formed, and this ammonia is removed,preferably by distillation, together with water vapor. Ammonia isseparated until more than 50% of that available is removed as determinedby difference from the original amount in the still and the amount ofammonia determined by analysis to be in the distillate stream. Generallyabout 60% to of total available ammonia is removed, the ammonia beingderived from the terephthalonitrile charged as well as intermediatesformed during the hydrolysis step. Then the molality of the terephthalicacid is adjusted either by further concentration of the liquid phase orby dilution with water until its molality is from about 1.5 to about2.5. This molality is readily determined by accounting for the waterremoved or added to the system whose molality is, of course, knowninitially. When this has been accomplished the terephthalic acid in thesystem is in solution or in slurry form and the system is saturated withcarbon dioxide by passing the gas in under pressure and the system thenallowed to cool from 200 to 300 C. down to to C. Alternatively, thesystem may be cooled first and then the CO added. This causes theterephthalic acid to precipitate and the free acid thus formed isseparated at 100 to 150 C. either by filtration, centrifugation or thelike while maintaining the system under carbon dioxide pressure of about50 to about 900 p.s.i.g. It will be understood that the carbon dioxidepressure is not critical as long as sufficient time and agitation areused to ensure CO saturation of the nitrile hydrolyzate solution. But itis important to maintain the CO pressure on both the filtrate and theseparated terephthalic acid during the separation step so as to preventdissociation of the ammonium carbonate and bicarbonate formed in thefiltrate. It will be understood that the filtrate may be recycled to theterephthalonitrile hydrolysis chamber, the CO being vented for recoveryand reuse for pressuring the system for isolation of the free acid. Theseparated terephthalic acid is found to be lower in nitrogen-containingproducts than a comparable hydrolysis procedure where CO is not used. Inorder to further illustrate the invention, the following examples aregiven:

EXAMPLES A 2-liter Parr reactor was charged with the appropriate amountof terephthalonitrile in 1.1 liters of water and heated at 280 to 300 C.for 0.33 to 1.0 hour. Then, the reactor was vented and ammonia removedby distillation at 250 C. until the desired amount was removed. Thereactor was then closed and pressured at 250 C. with 900 p.s.i.g. ofcarbon dioxide and the liquid in the system filtered at 100 C. whilemaintaining CO pressure on both the filtrate side and filter cake sideof a high pressure filter apparatus. After opening the system toatmospheric 3 pressure, the crude terephthalic acid was removed anddried at 110 C. overnight. The following table indicates the conditionsused and the results obtained:

4 saturating the system with carbon dioxide, isolating the precipitatedaromatic dicarboxyiic acid by separation under CO pressure of about 50to about 900 p.s.i.g.

TABLE I Comparison of crude TPA isolated at 100 C. with and withoutcarbonic acid Mole Total percent N b Percent N H4 percent N B3, Apercent Percent A percent vented l Percent N d N NH4 2 molal TPNhydrolyzate:

Without C02 90 0.59 O. 11 With CO2 90 0. 08 0. 51 0. 0. 41 Without CO 702. 59 1. 94: With 002.-.- 70 1. 86 0. 74 1. 15 0. 79 Without C0 50 6.4.45 With CO; 50 6. 28 +0.08 4. 75 +0.30 1 molal TPN hydrolyzat WithoutC0; 90 0. 11 0. 00 With CO2 90 0. 1O -0. 01 0. 00 0. 00 Without CO2..-70 0. 38 0. l7 With 002.-.... 70 0. 5O +0.12 0.25 +0. 08 Without CO50 1. 48 0. 60 With 002 50 3. 27 +1. 79 2, 46 +2.0

1 Based on tetephthalonitrile charged. b Determined by combustionanalysis.

' Weight percent nitrogen as NH4 determined by potentiometric titration.d A percent N =percent N in control less percent N in experiment withCO;

An analysis of the above table shows that at the 2 molal level, the useof CO for isolation of TPA results in a product of lower nitrogen whenthe amount of ammonia vented is above 50%. Venting at 50% actuallycaused a slight increase in total nitrogen when CO was used. The percentof NH ion in the system is likewise reduced with use of CO On the otherhand, with a 1 molal system no advantage with CO is seen.

As indicated, other aromatic dinitriles may be used in the process andthe preferred nitriles are terephthalonitrile, and2,6-dicyanonaphthalene. In the case of 2,6-dicyanonaphthalene, theprocess is carried out as described above, except that the molality ofthe vented system is preferably on the order of 1.5.

The invention claimed is:

1. A process for the preparation of an aromatic dicarboxylic acid whichcomprises subjecting an aromatic dinitrile of the benzene or naphthaleneseries to a non-catalytic aqueous hydrolysis in a closed reactor at 200C. to 300 C. until a hydrolysis equilibrium is obtained, venting theclosed system to remove more than 5 0% of available ammonia, adjustingthe vented system to a molality of the aromatic acid product from about1.5 to about 2.5,

2. The process of claim 1 where the nitrile is terephthalonitrile.

3. The process of claim 1 where the nitrile is 2,6-dicyanonaphthalene.

4. A process for the preparation of terephthalic acid by hydrolysis ofterephthalonitrile which comprises subjecting terephthalonitrile to anon-catalytic aqueous hydrolysis in a closed reactor at 200 C. to 300 C.until a hydrolysis equilibrium is obtained, venting the closed system toremove more than of available ammonia, adjusting the vented system to amolality of terephthalate from about 1.5 to about 2.5, saturating thesystem with carbon dioxide, and isolating the precipitated terephthalicacid by separation under CO pressure of about 50 to about 900 p.s.i.g.

References Cited FOREIGN PATENTS 428,020 3/1967 Japan 260-515 JAMES A.PATTEN, Primary Examiner

